1. Field of the Invention
The present invention relates to a half-duplex terminal for displaying a holding time and a communication method therefor, the half-duplex terminal having a transmitter/receiver for transmitting/receiving data and an acknowledgement (ACK) signal, a Push-To-X (PTX) key for activating data transmission/reception, a timer for counting time upon pressing of the PTX key, a display for displaying a total holding time and a controller for controlling calculation of the total holding time based on the time count, and display and counting down of the total holding time.
2. Description of the Related Art
Push-To-Talk (PTT) is an instant messenger service that allows a user to use a phone handset much like a traditional radio-based walkie-talkie. As implied from its name, the PTT service provides communication to the user with the touch of a PTT button. Compared to a traditional mobile phone, a PTT phone has a shorter connection time, thereby providing faster communication service.
The user can talk to many people simultaneously by making a PTT group call. The user who presses the PTT button first is able to speak with his/her handset while the remaining persons in the group can listen to the user with their handsets, unlike a normal phone where the user can speak to only one person at a time. With the PTT service, the user can launch either one-on-one or group conversations.
The current trend is for mobile terminals to operate over packet networks, and to instantly indicate whether reception is available to the other party through a screen.
PTT is based on half-duplex technology. A major example of half-duplex applications is a walkie-talkie. In view of the nature of the PTT service, once a call session is established, communication can only travel in one direction at a particular time. Therefore, if another person in the group wants to join the conversation, that person must wait until the current speaker stops talking. Time delay is inherent to the PTT service, because one must recognize that someone else has begun speaking. During the time delay period, many persons may attempt PTT transmission simultaneously. In this case, although their terminals send the transmission attempts to a PTT server, the PTT server sends an ACK message to the person whose terminal sent packets first in order to enable him/her PTT transmission, while sending non-acknowledgement (NACK) signals to the other users to prohibit them from transmitting PTT signals. In this fashion, the PTT service prevents many people from speaking at the same time.
A typical PTT call procedure will be described below with reference to FIG. 1. FIG. 1 is a diagram illustrating a signal flow over time for a PTT call.
Referring to FIG. 1, a first terminal 100 (terminal #1) sends PTT data 106 in packets D01 to D03 to a second terminal 104 (terminal #2) via a PTT server 102. The second terminal 104 then outputs the received PTT data 106. A transmission time delay 108 and a decoding time delay 110 exist until the PTT data 106 is output from the second terminal 104.
The second terminal 104 sends a reply 114 for the PTT data 106 in packets A01 to A03 to the first terminal 100 via the PTT server 102. A reply time delay 112 occurs before the reply transmission.
The first terminal 100 is held for a total holding time 116 between transmission of the PTT data 106 and reception of the reply 114.
As illustrated in FIG. 1, a PTT call is a semi-bidirectional communication. A total holding time elapses until a person receives a reply from a recipient of voice packets after he/she finishes speaking. The total holding time is the sum of a transmission time for voice packets to arrive at the receiving terminal via the PTT server, a decoding time for the receiving terminal to decode and output the PTT packets through a speaker, the time for the recipient to decide what to say before pressing the PTT button to reply, the time for voice packets as a reply to be transferred from the receiving terminal to the transmitting terminal via the PTT server, and the time for the transmitting terminal to decode the voice packets. If the total holding time is too long, the speaker is likely to determine that the recipient has made no reply; therefore, the speaker may attempt the same PTT transmission. Also, when excessive time is taken to decode PTT packets at the receiving terminal, during which the speaker attempts another PTT transmission, the recipient must inconveniently wait until he/she receives the same message and is authorized to reply. This problem will be addressed below with reference to FIG. 2.
FIG. 2 is a diagram illustrating a signal flow when a reply is cancelled at a PTT call.
Referring to FIG. 2, the first terminal 100 sends the PTT data 106 in the packets D01 to D03 to the second terminal 104 via the PTT server 102. The second terminal 104 then outputs the received PTT data 106. The transmission time delay 108 and the decoding time delay 110 elapse until the PTT data 106 is output from the second terminal 104.
If the first terminal 100 sends retransmission PTT data 200 without receiving the reply 114 for the PTT data 106 and the second terminal 104 receives the retransmission PTT data 200 before the packets A01 and A02 of the reply 114 arrive at the first terminal 100, the PTT server 102 cancels the transmission of the reply packets A01 and A02 and sends a retransmission packet D04 to the second terminal 104. The second terminal 104 cancels the reply 114 and outputs the retransmission data 200.
This problem is exacerbated under a weak electric field or a bad propagation condition.